Lightweight linear motor

ABSTRACT

A linear motor for the positioning of objects such as magnetic pickup heads and the like comprising a support structure that mounts a guide rod, an annular permanent magnet, and a concentric pole piece that is spaced from the magnet. A voice coil assembly slidably engages the rod and a cylindrical surface of the pole piece and slides linearly along the rod and the surface into and out of an annular space between the magnets. An electric conductor is wound about a lightweight sleeve of the coil assembly and connected with an electric power source for generating electromagnetic forces and linearly moving the motor. The coil assembly includes means for mounting the pickup head or the like and an arm that extends radially away from the assembly into engagement with a guide track on the support structure to prevent rotary motions of the coil assembly on the rod or the cylindrical surface.

' OTHER PUBLICATIONS Rexford High Force Constant Voice Coil Motor ForRapid Seek IBM Technical Disclosure Bulletin, Vol.

12, No. 12, 5/1970 p. 2273.

Primary Examiner.l. D. Miller Assistant ExaminerH. HuberfeldAttorneyStephen S. Townsend et al.

.582 BR 3e760s2fl6 unrteu DIHIBS ratent l 1 l 11 3,760,206 Hertrich 1Sept. I8, 1973 LIGHTWEIGHT LINEAR MOTOR [57] ABSTRACT [75] Inventor:Friedrich Hertrich Boulder A linear motor for the ositionin of ob'ectssuch as C I P 8 l o magnetic pickup heads and the like comprising a sup-[73] Assignee: Iomec, Inc., Santa Clara, Calif. port structure thatmounts a guide rod, an annular permanent magnet, and a concentric polepiece that is [22] 1972 spaced from the magnet. A voice coil assemblyslidably [21] Appl. No.: 217,119 v engages the rod and a cylindricalsurface of the pole piece and slides linearly along the rod and thesurface 31011103561325; into and out of an annular space between themagnets. Fie'Id 687 38' An electric conductor is wound about alightweight 310/12 15 sleeve of the coil assembly and connected with anelectric power source for generating electromagnetic [56] R f ren s C dforces and linearly moving the motor. The coil assem- UNITED STATESPATENTS bly includes means for mounting the pickup head or the 9,197]Swrman 8/135 X like and an arm that extends radially away from theassembly into engagement with a guide track on the support structure toprevent rotary motions of the coil assembly on the rod or thecylindrical surface.

19 Claims, 4 Drawing Figures ELECTRIC POWER SOURCE PAIENTEDSEP! 8 I915.3', 760.206

SHEU 1 0f 2 ELECTRIC POWER SOURCE LIGHTWEIGHT LINEAR MOTOR BACKGROUND OFTHE INVENTION Conventional linear motors for positioning transducers andthe like such as electromagnetic pickup heads used on disk memories arerelatively intricate and complicated mechanisms that are costly toproduce, require a high degree of maintenance, have a relatively highfail-rate and which sometimes lack the required accuracy. For example, aconventional prior art motor for the positioning of a pickup headweighing between and grams has a total moving mass of between 800 to 900grams. The relatively large weight requires positioning and guidancedevices capable of supporting the large weight. In addition, such linearmotors have large inertias which make it difficult to substantiallyinstantaneously stop the linear motor as is required for the high speedpositioning of the recording head.

A major reason for the excessively large ratio between motor dead weightand actual payload has been the difficulty of designing a motor annaturewith high precision linear guiding and the required mechanical stiffnessfor high performance, e.g., high speed operation. To arrive at thedesired stiffness the armatures were enlarged and constructed of highstrength materials such as aluminum castings. The resulting, relativelyheavy armature dictated the use of low friction ball and/or needlebearings to reduce drag and to eliminate the possibility of prematurewear of the moving surfaces.

The use of ball and roller bearings required relatively massive hardwarefor rigidly mounting them which further increased the moving mass. Asidefrom the experienced mechanical difficulties briefly set forth abovethis such prior art linear motors set more stringent demands on poweramplifiers, power supplies and the cooling of the associated circuitry,thus making the motor more complex and further increasing its costs;

SUMMARY OF THE INVENTION The present invention provides a lightweightlinear motor for electromagnetic pickup heads and the like which has ahigh response rate and which is constructed of simple, readily availablecomponents. As a result, the motor enables substantial cost reductionsas compared to linear motors of comparable capacities constructed inaccordance with the prior art. The simplicity of the motor reducesmanufacturing costs as well as maintenance costs and virtuallyeliminates breakdowns and ensuing system downtimes.

Generally speaking, a linear motor constructed in accordance with theinvention comprises a support structure with a central linear guide rodand a voice coil assembly linearly movable along the rod. A magnet andan associated pole piece, respectively, are disposed on each side of thevoice coil and define a space into which the coil slides during linearmovements. The magnet or the pole piece defines a cylindrical surfacethat is concentric with the guide rod. Sliding bearing means such asbronze or teflon sleeve bearings mount the coil assembly to the rod andthe cylindrical surface for support and guidance.

The coil assembly is preferably a lightweight, thinwalled plastic tubeabout which a conductor is coiled. A first end of the tube is providedwith a guide ring that supports that end on the cylindrical surface andthe other end of the tube is mounted to a carriage slidable along theguide rod. The carriage is a simple, low-cost plastic molding andincludes an arm that extends radially away and slidably engages a guidetrack integrally constructed with the support structure. The guide trackprevents rotational movements of the coil assembly.

A linear motor constructed in accordance with the invention of acapacity comparable to that of the above described prior art motor forpositioning 10-20 gram electromagnetic pickup heads has a movablearmature weight of no more than approximately grams, a roughly IO-to-lweight reduction. This is possible by constructing the armature ofthin-walled, lightweight materials which are shaped to exhibitsubstantial rigidness while having very little weight; by providing arigid, high precision yet low cost guide rod along which the armaturemoves; by utilizing a cylindrical surface of one of the magnets or thepole piece, preferably the convexly cylindrical surface of the polepiece over which the armature moves when it is protracted, for aligningand guiding the coil assembly; and further by replacing the prior artball and roller bearings with lightweight slide bearings. This lastaspect of the invention is primarily possible due to the overall weightreduction and further contributes to the low weight of the movablearmature by eliminating the priorart need for massive roller or ballbearing mounts.

As a consequence of the many advantages afforded by the presentinvention the dead-weight to payload ratio can be lowered to a morereasonable 1:4 to about 1:8 as compared with the prior art ratio of 1:40to about 1:80. Moreover, complicated mounting of intricate bearings andguideways, expensive machining and critical tolerances, all of whichrender prior art linear motors very expensive to construct and maintain,can be eliminated so that a linear motor constructed in accordance withthe invention can be produced at relatively low costs.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. -1 is a plan view of a linearmotor constructed in accordance with the invention;

FIG. 2 is a side elevation, in section, of the motor illustrated in FIG.1 and is taken on line 22 of FIG. 1;

FIG. 3 is a front elevational view of the motor illustrated in FIG. 1;and

FIG. 4 is an enlarged, partially schematic illustration of the voicecoil assembly of the motor of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 and 2, alinear motor 6 for positioning objects such as an electromagnetictransducer 8 along a straight line 10 broadly comprises a supportstructure 12, a linearly movable voice coil assembly 14 carried by thesupport structure and a magnet assembly 16. The voice coil assemblyincludes a coiled conductor 18 (see FIG. 4) connected to an electricpower source 20. Upon energization of the coiled conductor anelectromagnetic force is created which reacts with the magnet assemblyand moves the coil assembly back or forth according to the polarity ofthe current supplied to the conductor. To measure relative movements alinear position transducer 22 is normally provided.

The above described operation of the linear motor is conventional.

Referring now to FIGS. 1 through 3, support structure 12 comprises aflat base 24 which includes a perpendicular, integrally constructed endbracket 26 and, at the opposite end of the base, an end plate 28 that isdowled and bolted to the base. The end plate and the bracket includeprecision aligned openings 30 through which an elongate,precision-ground straight guide rod 32 extends. The rod is suitablysecured to the support structure as with a bolted-on spring clamp 34.

End plate 28 includes two circular shoulders 36, 38 which are concentricwith bore 30 and, therefore, with guide rod 32. The inner shoulder 36engages and centers a cylindrically tubular pole piece 40 of magnetassembly 16. A cylindrical magnet 42 of the magnet assembly is securedto a motor shell 44 which engages and is centered by the outer circularshoulder 38 of end plate 28. The pole piece acts as a return path forthe flux lines of magnet 42 and as a support and guide for coil assembly14 as described in detail below.

The pole piece and the magnet extend in the direction of guide rod 32and have a length no more than and usually slightly less than aboutone-half the guide rod length so that they terminate at about the midwaypoint of the guide rod. Both have about the same length although thepole piece is preferably slightly longer and acts as a stop for the coreassembly. A disk 46 is slipped over the guide rod and anchored .in aninterior bore 48 of pole piece 40 to position align an outer convexsurface 50 of the pole piece with the guide rod. The convex surface hasa high quality finish and acts as a bearing surface for one end of thecoil assembly.

The magnet preferably comprises a relatively low weight permanentceramic magnet and the circular shoulders on end plate 28 are arrangedso that the pole piece and the magnet are spaced apart to define arelatively narrow and deep or elongate annular space 52 between theminto which voice coil assembly 14 can 'move as illustrated in FIG. 2.

Referring now to FIGS. 1 through 4, the voice coil assembly isconstructed of a thin, lightweight epoxy tube 54 having a wall thicknessof no more than about 0.031 inches and which has a length about equal toor slightly greater than the length of pole piece 40. A bearing end ring56 is bonded to the inner end of the epoxy tube. The end ring isconstructed of a lowfriction material such as self-lubricating bronze,teflon or the like.

Conductor coils 18 extend from adjacent end ring 56 a limited distancetowards the other end of tube 54 so that the coils are in annular space52 irrespective of the relative position of coil assembly 14 between theterminal points of its travel along rod 32. Leads 58 extend forward fromthe coiled conductor and are secured to a terminal bar 60 for connectionto power source 20. The terminal bar is mounted to a carriage 62 whichis in turn bonded to the other end of tube 54.

To reduce the overall weight of the coil assembly carriage 62 isconstructed of relatively lightweight plastic and is injection molded toassure low cost. it comprises a disk or center portion 64 that has a hub66 into which a low-friction sleeve bearing ring constructed ofselflubricating porous metal, Teflon or the like is pressed. The bearingring is concentric with an end ring 56 mounted at the other end of tube54. The hub also includes an upwardly facing flat surface 70 formounting a spring arm 72 or the like to which transducer 8 is secured.

Carriage 62 has a downwardly depending arm 74 which extends radiallyaway from hub 66 and which terminates in an end member 76 that includestwo oppositely directed faces to which low friction padding 78 isapplied. The padding is disposed between two upwardly orientedprotrusions 80 which are spaced apart to define a U-shaped channel andwhich engage the padding to prevent rotational movements of the carriageand, therewith, of coil assembly 14 about guide rod 32 while pennittinglinear longitudinal movement of the carriage along the rod. Forsimplicity the protrusions are integrally constructed with base 12.

For purposes more fully set forth hereinafter center portion 64 includesa plurality of circumferentially spaced apertures 82 which communicateone side of the center portion with the other. The apertures permit afree air flow and facilitate the operation of the linear motor. When thecoil assembly is at its left-most position (as seen in FIG. 2) andcenter portion 64 is clearly adjacent annular space 52, linear coilassembly movements do not result in a vacuum or a pressure build-up inthe annular space because air can freely communicate through apertures82.

Turning now to the assembly and operation of the linear motor of thepresent invention and referring to FIGS. 1 through 4, pole piece 40 isbonded to end plate 28 with a suitable epoxy or the like in a precisionjig to assure precise alignment and concentricity between end plate bore30 and convex surface 50 of the motor center. Thereafter the motor shell44 with magnet 42 is secured to the end plate by placing motor shelf 44over the outer shoulder and bonding it to the end plate.

Guide rod 32 is inserted through one of the bores 30, disk 46 is placedover the guide rod and positioned with a retaining ring (not shown) orthe like and voice coil assembly 14 is slipped over the unsupportedguide rod end. Resilient rings such as rubber O-rings 84 are placed overguide rod 32 against the outer side of disk 46. Bearing ring 56 isslipped over the polished cylindrical pole piece surface 50 and bearingring 68 over the guide rod and the guide rod is anchored in bores 30with clip 34 or the like. The rubber O-rings serve as a resilient stopwhen the carriage moves to the left, as viewed in FIG. 2, and therebyreduce deceleration forces.

Power source 20 is now connected with leads 58 via terminal bar 60,spring arm 72 with transducer 8 is secured to the carriage and thecarriage is positioned so that arm 74 is retained between baseprotrusions 80.

The linear motor of the present invention is now ready for operation.Energization of the coiled conductor 18 moves the coil assembly alongthe guide rod and the convex pole piece surface by virtue of theelectromagnetic field generated by the conductor. Reversal of thecurrent permits reversal of the direction of motor movement. The linearposition transducer 22 is suitably connected with controls (not shown)for energizing and/or de-energizing the coiled conductor when it reachesa desired point along its linear travel.

When the voice coil assembly is energized and moved along the guide roda relatively small mass is in motion. The carriage is a lightweightplastic injection molding, tube 54 is a thin-walled lightweightepoxy-glass tube which mounts the required conductor coils and one ofthe simple, narrow and lightweight bearing rings. The

ticularly when compared to the required supporting structure for ball orroller bearings, is mounted to carriage hub 62. In spite of thelightweight construction, unacceptable deflection of the coil assemblyis prevented because the components of the coil assembly are constructedof rigid materials because they are epoxy-bonded to each other to form aunitary, integral and high-strength unit, and because the coil assemblyis carried by lightweight bearing sleeves instead of relatively heavyball or roller bearings that need a great deal of structural support. Inthis manner the heretofore large moving mass of linear motors is greatlyreduced. The resulting motor of the invention is of much lower weight,has a much higher response rate and can be manufactured at a costsignificantly less than the cost of comparable prior art motors.

I claim:

l. A linear positioning motor comprising:

a support structure including a central linear guide rod extending overthe full effective length of the support structure and further includingchannel means spaced from and parallel to the rod and extending over atleast a portion of the rod length;

a voice coil assembly:

means mounting the voice coil assembly for linear movements along therod;

magnet means spaced from and parallel to the rod extending over aportion of the rod length;

means connected with the assembly and extending into the channel meansto prevent rotational movements of the assembly; and

means for subjecting the assembly to current for moving the assemblyalong the rod.

2. A motor according to claim 1 wherein the magnet means includes asurface parallel to the rod, and including means supporting a portion ofthe assembly on the surface during all movements of the assembly alongthe rod.

3. A motor according to claim 1 wherein the assembly mounting meanscomprises sleeve bearings.

4. A low-cost, lightweight linear motor for accurately positioning arecording head or the like along a straight line comprising:

a support structure;

magnet means secured to the structure and defining an annular elongatespace;

an annular electric coil assembly insertable into the annular space;

sliding bearing means affixed to said assembly for supporting a portionof the assembly on said magnet means and permitting linear assemblymovements along the axis of the annular space and means for mounting therecording head or the like to an end of the assembly.

5. A motor according to claim 4 including a guide rod secured to thesupport structure and disposed concentrically with the annular space,wherein the assembly includes carriage means disposed at one end of theassembly, and wehrein the sliding bearing means includes a first sleevebearing disposed adjacent another end of the assembly, and a secondsleeve bearing secured to the carriage means and engaging the rod forslidable movement therealong.

6. A motor according to claim 5 including bar means projecting from thestructure and oriented parallel to the guide rod, and including slidingpads mounted to the carriage means engaging the bar means and preventingrotational movements of the carriage means and the assembly about theconcave surface and the guide rod.

7. A motor according to claim 4 including a guide rod secured to thesupport structure concentrically with the annular space and having alength at least about twice the length of the annular space, wherein themagnet means is defined by an outer annular magnet and an inner annularmagnet pole piece spaced from the outer magnet to define the annularspace, the pole piece being further spaced from the guide rod, meansconcentrically supporting the magnet and the pole piece, the supportingmeans including disk means facing in the direction of the guide rod, andwherein the coil assembly includes a carriage slidable along the guiderod between a free end thereof and the disk means for supporting one endof the coil assembly.

8. A motor according to claim 7 including at least one annular stop ringdisposed about the guide rod and resting against the disk means forlimiting the movement of the coil assembly, the stop ring beingconstructed of a resilient material to limit the deceleration forceswhen the moving carriage means engages the ring.

9. A lightweight linear motor for precision positioning an object alonga straight line comprising a support structure, a guide rod having endssecured to the support structure and an intermediate portion spaced fromthe structure, an annular pole piece having a lesser length than theguide rod and a first end secured to the support structure adjacent apoint where an end of the guide rod is secured to the structure, thepole piece extending in the direction of the rod and having a freesecond end, an annular magnet having a first end secured to the supportstructure adjacent the point, the magnet terminating at a second endapproximately aligned with the second end of the pole piece, the polepiece and the magnet being spaced from each other to define an annularspace between them defined by at least one cylindrical surface which isconcentric with the rod, an annular voice coil assembly having a lesserlength than the rod, and being dimensioned to be insertable into theannular space, one end of the assembly including a first sliding sleeveengaging the cylindrical surface for guidance during linear slidablemovements of the assembly, another end of the assembly being defined bya carriage having a second sleeve bearing in sliding engagement with therod for linear slidable movement therealong and an arm extendinggenerally radially away from the bearing towards the support structure,at least one elongate protrusion parallel to the rod defined by thesupport structure, means defined by the arm for preventingrotational.movements of the assembly, means for securing the object tothe carriage, a conductor secured to the assembly and dimensioned to bedisposed within the annular space at all operative positions of theassembly in the annular space, and means for supplying the conductorwith electric current so that an electromotive force generated betweenthe conductor and the magnets linearly moves the assembly along the rodand the cylindrical surface.

10. A motor according to claim 9 wherein the carriage comprises alightweight plastic molding.

11. A motor according to claim 10 wherein th molding is defined by adisk portion disposed about the rod, and wherein the arm extendsradially outwardly from the disk portion, the disk portion defining ahub mounting the second bearing to the carriage and a plurality ofapertures permitting air communication from one side of the disk portionto the other side to prevent the formation of a vacuum or the build-upof pressure within spaces enclosed by the magnets during operation ofthe motor.

12. A motor according to claim 11 wherein the assembly includes atubular plastic shell insertable into the annular space, and wherein theconductor is wound about the exterior of the plastic shell.

13. A motor according to claim 12 including means supporting the freesecond end of the pole piece on the rod, and including at least oneresilient O-ring disposed on the side of the last mentioned means facingtowards the carriage for providing a resilient stop limiting slidablemovements of the carriage towards the pole piece and reducing thedeceleration forces to which the carriage is exposed. like 14. A motoraccording to claim 9 wherein the magnet comprises a permanent ceramicmagnet, wherein the pole piece defines the cylindrical surface in theform of a concave surface, and wherein the first bearing slidablyengages the concave surface of the pole piece.

15. A motor according to claim 9 wherein the protrusion comprises a pairof parallel, spaced apart protrusions constructed integrally with thesupport structure and defining parallel opposing faces extendingparallel to the rod, and wherein the arm includes an end portion andfriction pads positioned to engage and slide along the parallelprotrusion faces to thereby prevent rotational movements of the assemblyabout the rod.

16. A motor according to claim 9 wherein the support structure includesan end plate demountably fastened to a base plate and extendingsubstantially perpendicularly away therefrom, the end plate includingfirst and second annular shoulders for securing the magnets to the endplate, and a bore concentric with the shoulders for engaging the guiderod, and including 8, means demountably fastening the magnets and theguide bar to the support structure.

17. A linear positioning motor, comprising: a support structureincluding a central linear guide rod; magnet means spaced from andconcentric with said guide rod and extending over at least a portion ofthe rod length, said magnet means defining an annular channel spacedoutwardly from said rod; a voice coil assembly adapted for movementwithin said channel axially of said rod;

slidable bearing means associated with said assembly.

and mounting at least a portion of said assembly on said magnet meansfor reciprocal linear movement within said channel; and

means for subjecting said assembly to electrical current for movementwithin said channel.

18. A motor according to claim 17, wherein said slidable bearing meanscomprises at least one sleevebearing affixed to at least a portion ofthe interior surface of said voice coil assembly and adapted forslidable movement along a convex surface of said magnet means defining awall of said annular channel.

19. A linear positioning motor comprising:

a support structure including a central linear guide rod;

a voice coil assembly;

means slidably mounting a portion of the voice coil assembly on the rodfor linear movement therealong;

magnet means parallel to and spaced outwardly from the rod and extendingover a portion of the rod length;

means slidably mounting another portion of the voice coil assembly on asurface of the magnet means for linear movement therealong; and meansfor subjecting the assembly to current for moving the asselnblgy alongthe rod.

1. A linear positioning motor comprising: a support structure includinga central linear guide rod extending over the full effective length ofthe support structure and further including channel means spaced fromand parallel to the rod and extending over at least a portion of the rodlength; a voice coil assembly: means mounting the voice coil assemblyfor linear movements along the rod; magnet means spaced from andparallel to the rod extending over a portion of the rod length; meansconnected with the assembly and extending into the channel means toprevent rotational movements of the assembly; and means for subjectingthe assembly to current for moving the assembly along the rod.
 2. Amotor according to claim 1 wherein the magnet means includes a surfaceparallel to the rod, and including means supporting a portion of theassembly on the surface during all movements of the assembly along therod.
 3. A motor according to claim 1 wherein the assembly mounting meanscomprises sleeve bearings.
 4. A low-cost, lightweight linear motor foraccurately positioning a recording head or the like along a straightline comprising: a support structure; magnet means secured to thestructure and defining an annular elongate space; an annular electriccoil assembly insertable into the annular space; sliding bearing meansaffixed to said assembly for supporting a portion of the assembly onsaid magnet means and permitting linear assembly movements along theaxis of the annular space and means for mounting the recording head orthe like to an end of the assembly.
 5. A motor according to claim 4including a guide rod secured to the support structure and disposedconcentrically with the annular space, wherein the assembly includescarriage means disposed at one end of the assembly, and wehrein thesliding bearing means includes a first sleeve bearing disposed adjacentanother end of the assembly, and a second sleeve bearing secured to thecarriage means and engaging the rod for slidable movement therealong. 6.A motor according to claim 5 including bar means projecting from thestructure and oriented parallel to the guide rod, and including slidingpads mounted to the carriage means engaging the bar means and preventingrotational movements of the carriage means and the assembly about theconcave surface and the guide rod.
 7. A motor according to claim 4including a guide rod secured to the support structure concentricallywith the annular space and having a length at least about twice thelength of the annular space, wherein the magnet means is defined by anouter annular magnet and an inner annular magnet pole piece spaced fromthe outer magnet to define the annular space, the pole piece beingfurther spaced from the guide rod, means concentrically supporting themagnet and the pole piece, the supporting means including disk meansfacing in the direction of the guide rod, and wherein the coil assemblyincludes a carriage slidable along the guide rod between a free endthereof and the disk means for supporting one end of the coil assembly.8. A motor according to claim 7 including at least one annular stop ringdisposed about the guide rod and resting against the disk means forlimiting the movement of the coil assembly, the stop ring beingconstructed of a resilient material to limit the deceleration forceswhen the moving carriage means engages the ring.
 9. A lightweight linearmotor for precision positioning an object along a straight linecomprising a support structure, a guide rod having ends secured to thesupport structure and an intermediate portion spaced from the structure,an annular pole piece having a lesser length than the guide rod and afirst end secured to the support structure adjacent a point where an endof the guide rod is secured to the structure, the pole piece extendingin the direction of the rod and having a free second end, an annularmagnet having a first end securEd to the support structure adjacent thepoint, the magnet terminating at a second end approximately aligned withthe second end of the pole piece, the pole piece and the magnet beingspaced from each other to define an annular space between them definedby at least one cylindrical surface which is concentric with the rod, anannular voice coil assembly having a lesser length than the rod, andbeing dimensioned to be insertable into the annular space, one end ofthe assembly including a first sliding sleeve engaging the cylindricalsurface for guidance during linear slidable movements of the assembly,another end of the assembly being defined by a carriage having a secondsleeve bearing in sliding engagement with the rod for linear slidablemovement therealong and an arm extending generally radially away fromthe bearing towards the support structure, at least one elongateprotrusion parallel to the rod defined by the support structure, meansdefined by the arm for preventing rotational movements of the assembly,means for securing the object to the carriage, a conductor secured tothe assembly and dimensioned to be disposed within the annular space atall operative positions of the assembly in the annular space, and meansfor supplying the conductor with electric current so that anelectromotive force generated between the conductor and the magnetslinearly moves the assembly along the rod and the cylindrical surface.10. A motor according to claim 9 wherein the carriage comprises alightweight plastic molding.
 11. A motor according to claim 10 whereinth molding is defined by a disk portion disposed about the rod, andwherein the arm extends radially outwardly from the disk portion, thedisk portion defining a hub mounting the second bearing to the carriageand a plurality of apertures permitting air communication from one sideof the disk portion to the other side to prevent the formation of avacuum or the build-up of pressure within spaces enclosed by the magnetsduring operation of the motor.
 12. A motor according to claim 11 whereinthe assembly includes a tubular plastic shell insertable into theannular space, and wherein the conductor is wound about the exterior ofthe plastic shell.
 13. A motor according to claim 12 including meanssupporting the free second end of the pole piece on the rod, andincluding at least one resilient O-ring disposed on the side of the lastmentioned means facing towards the carriage for providing a resilientstop limiting slidable movements of the carriage towards the pole pieceand reducing the deceleration forces to which the carriage is exposed.like
 14. A motor according to claim 9 wherein the magnet comprises apermanent ceramic magnet, wherein the pole piece defines the cylindricalsurface in the form of a concave surface, and wherein the first bearingslidably engages the concave surface of the pole piece.
 15. A motoraccording to claim 9 wherein the protrusion comprises a pair ofparallel, spaced apart protrusions constructed integrally with thesupport structure and defining parallel opposing faces extendingparallel to the rod, and wherein the arm includes an end portion andfriction pads positioned to engage and slide along the parallelprotrusion faces to thereby prevent rotational movements of the assemblyabout the rod.
 16. A motor according to claim 9 wherein the supportstructure includes an end plate demountably fastened to a base plate andextending substantially perpendicularly away therefrom, the end plateincluding first and second annular shoulders for securing the magnets tothe end plate, and a bore concentric with the shoulders for engaging theguide rod, and including means demountably fastening the magnets and theguide bar to the support structure.
 17. A linear positioning motor,comprising: a support structure including a central linear guide rod;magnet means spaced from and concentric with said guide rod andextending over at least a portion of the rod length, said magnet meansdefining an annular channel spaced outwardly from said rod; a voice coilassembly adapted for movement within said channel axially of said rod;slidable bearing means associated with said assembly and mounting atleast a portion of said assembly on said magnet means for reciprocallinear movement within said channel; and means for subjecting saidassembly to electrical current for movement within said channel.
 18. Amotor according to claim 17, wherein said slidable bearing meanscomprises at least one sleeve-bearing affixed to at least a portion ofthe interior surface of said voice coil assembly and adapted forslidable movement along a convex surface of said magnet means defining awall of said annular channel.
 19. A linear positioning motor comprising:a support structure including a central linear guide rod; a voice coilassembly; means slidably mounting a portion of the voice coil assemblyon the rod for linear movement therealong; magnet means parallel to andspaced outwardly from the rod and extending over a portion of the rodlength; means slidably mounting another portion of the voice coilassembly on a surface of the magnet means for linear movementtherealong; and means for subjecting the assembly to current for movingthe assembly along the rod.